You two have different goals... why run the race together when you're running in opposite directions?
I read all the posts in this thread and haven't changed my belief that if two people are not on the same track with marriage/not marriage, they have no future. You said it yourself. You know that your future with this guy is to remain as you are--that is until he finds someone else.
It is obvious that you value the commitment that comes with marriage; he doesn't. I don't see how those two diametrically opposite opinions can foster a healthy relationship.
If you want to continue living in the dream world that he will one day change his mine, that is your choice. But, if it was me, I'd tell him that you want a future, you don't want just now.
You don't want someone who is leaving the door open for if he finds someone better, you want someone who knows that you're "it."
And it is not wrong to want that.
